New United States government recommendations for energy conservation through reduction of lighting levels, as well as escalating costs of electrical energy, make the use of daylight in buildings, when available, highly desirable. A casual inspection of many office buildings will show that lighting fixtures are on while the contributed daylight through the windows makes the use of at least a part of the interior lighting unnecessary.
Common methods of construction today employ suspended ceilings with fluorescent lay-in or troffer-type fixtures supported on such ceilings. Popular fixtures are the four-lamp fluorescent type, usually with two ballast transformers. It is desirable to control at least one of these ballasts and its two lamps by photoelectric response to daylight. Photocell controlled relays are well known in the art, but a relay of this type, installed within the wiring and ballast compartment of a fixture, requires a simple method of access to the daylight upon which its operation depends.